A baby born before 37 weeks gestation (the time from conception to birth) is considered premature; when born before 32 weeks, a child is considered significantly premature.

term used to describe infants born before 37 weeks. Normal clinical gestation is 40 weeks (which is usually 36-38 weeks embryonic development) infants born after 42 weeks clinical gestation are called postmature. (More? Normal Development - Birth)

describes a baby born before 37 weeks of pregnancy.

(infant) - an infant born before 37 weeks gestation

Happening, arriving, existing, or performed before the proper or usual time; adopted too soon; too early; untimely; as, a premature fall of snow; a premature birth; a premature opinion; premature decay.

Arriving or received without due authentication or evidence; as, a premature report.

uncommonly early or before the expected time; "illness led to his premature death"; "alcohol brought him to an untimely end"

A hasty move, maneuver or plan. To take action without sufficient preparation.

too soon or too hasty; "our condemnation of him was a bit previous"; "a premature judgment"

A hasty move or series of moves or plan, or to act without enough preparation.